Change in coreboot[master]: drivers/pc80/rtc: Make use of legacy BIOS checksum configurable

[Nico Huber (Code Review)]

Nico Huber has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/56215 )

Change subject: drivers/pc80/rtc: Make use of legacy BIOS checksum configurable
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drivers/pc80/rtc: Make use of legacy BIOS checksum configurable

The legacy BIOS checksum has a fixed location amidst CMOS and often
conflicts with our option tables. Oddly, we only ever handle it when
USE_OPTION_TABLE is selected. Let's disable it by default and if
nobody complains, remove it later.

Change-Id: If6512b019c3cc0441db311a3b590ab67b8db27f3
Signed-off-by: Nico Huber 
---
M src/drivers/pc80/rtc/Kconfig
M src/drivers/pc80/rtc/mc146818rtc.c
2 files changed, 14 insertions(+), 3 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/15/56215/1

diff --git a/src/drivers/pc80/rtc/Kconfig b/src/drivers/pc80/rtc/Kconfig
index 7958682..a8c6f38 100644
--- a/src/drivers/pc80/rtc/Kconfig
+++ b/src/drivers/pc80/rtc/Kconfig
@@ -9,3 +9,12 @@
    depends on DRIVERS_MC146818
    help
      May be useful for legacy OSs that assume its presence.
+
+config USE_PC_CMOS_CHECKSUM
+	bool "Maintain legacy-BIOS checksum in CMOS"
+	default y if !USE_OPTION_TABLE
+	depends on DRIVERS_MC146818 && USE_OPTION_TABLE
+	help
+	  May be useful for legacy OSs that assume its presence. Also,
+	  Linux' /dev/nvram checks it (but seems incompatible to our
+	  option table).
diff --git a/src/drivers/pc80/rtc/mc146818rtc.c b/src/drivers/pc80/rtc/mc146818rtc.c
index e0c2400..a26ae2d 100644
--- a/src/drivers/pc80/rtc/mc146818rtc.c
+++ b/src/drivers/pc80/rtc/mc146818rtc.c
@@ -86,7 +86,7 @@
    /* See if there has been a CMOS power problem. */
    cmos_invalid = cmos_error();

-	if (CONFIG(USE_OPTION_TABLE)) {
+	if (CONFIG(USE_PC_CMOS_CHECKSUM)) {
    	/* See if there is a CMOS checksum error */
    	checksum_invalid = !cmos_checksum_valid(PC_CKS_RANGE_START,
    					PC_CKS_RANGE_END, PC_CKS_LOC);
@@ -128,8 +128,10 @@
    	if (checksum_invalid)
    		printk(BIOS_DEBUG, "RTC: coreboot checksum invalid\n");

-		/* Make certain we have a valid checksum */
-		cmos_set_checksum(PC_CKS_RANGE_START, PC_CKS_RANGE_END, PC_CKS_LOC);
+		if (CONFIG(USE_PC_CMOS_CHECKSUM)) {
+			/* Make certain we have a valid checksum */
+			cmos_set_checksum(PC_CKS_RANGE_START, PC_CKS_RANGE_END, PC_CKS_LOC);
+		}
    }

/* Clear any pending interrupts */